Drop Dynamics on Liquid-Infused Surfaces: The Role of the Lubricant Ridge.

We employ a free-energy lattice-Boltzmann method to study the dynamics of a ternary fluid system consisting of a liquid drop driven by a body force across a regularly textured substrate, infused by a lubricating liquid. We focus on the case of partial wetting lubricants and observe a rich interplay between contact line pinning and viscous dissipation at the lubricant ridge, which become dominant at large and small apparent angles, respectively. Our numerical investigations further demonstrate that the relative importance of viscous dissipation at the lubricant ridge depends on the drop to lubricant viscosity ratio, as well as on the shape of the wetting ridge.

Fabrication and Wettability Study of WO3 Coated Photocatalytic Membrane for Oil-Water Separation: A Comparative Study with ZnO Coated Membrane.

Superhydrophilic and underwater superoleophobic surfaces were fabricated by facile spray coating of nanostructured WO3 on stainless steel meshes and compared its performance in oil-water separation with ZnO coated meshes. The gravity driven oil-water separation system was designed using these surfaces as the separation media and it was noticed that WO3 coated stainless steel mesh showed high separation efficiency (99%), with pore size as high as 150 µm, whereas ZnO coated surfaces failed in the process of oil-water separation when the pore exceeded 50 µm size. Since, nanostructured WO3 is a well known catalyst, the simultaneous photocatalytic degradation of organic pollutants present in the separated water from the oil water separation process were tested using WO3 coated surfaces under UV radiation and the efficiency of this degradation was found to be quite significant. These results assure that with little improvisation on the oil water separation system, these surfaces can be made multifunctional to work simultaneously for oil-water separation and demineralization of organic pollutants from the separated water. Fabrication of the separating surface, their morphological characteristics, wettability, oil water separation efficiency and photo-catalytic degradation efficiency are enunciated.

Study of factors governing oil-water separation process using TiO2 films prepared by spray deposition of nanoparticle dispersions.

Surfaces which possess extraordinary water attraction or repellency depend on surface energy, surface chemistry, and nano- and microscale surface roughness. Synergistic superhydrophilic-underwater superoleophobic surfaces were fabricated by spray deposition of nanostructured TiO2 on stainless steel mesh substrates. The coated meshes were then used to study gravity driven oil-water separation, where only the water from the oil-water mixture is allowed to permeate through the mesh. Oil-water separation efficiencies of up to 99% could be achieved through the coated mesh of pore sizes 50 and 100 µm, compared to no separation at all, that was observed in the case of uncoated meshes of the same material and pore sizes. An adsorbed water on the TiO2 coated surface, formation of a water-film between the wires that form the mesh and the underwater superoleophobicity of the structured surface are the key factors that contribute to the enhanced efficiency observed in oil-water separation. The nature of the oil-water separation process using this coated mesh (in which the mesh allows water to pass through the porous structure but resists wetting by the oil phase) minimizes the fouling of mesh so that the need for frequent replacement of the separating medium is reduced. The fabrication approach presented here can be applied for coating large surface areas and to develop a large-scale oil-water separation facility for oil-field applications and petroleum industries.